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John from PA

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Reply with quote  #16 
See what might be useful at https://www.maintenance.org/search?searching=true&type=0-topics&queryString=dynamic+absorber
MarkL

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Reply with quote  #17 
Seen a simple one made with a piece of rod and a sliding weight, rudimentary looking but was 'tuneable' I think Electric Pete also had a load of Information on them on the Old site?

Didn't sees Johns reply before I posted mine. 
I see Pete has some top[ics in that thread list 
Dave Reynolds

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Reply with quote  #18 
Batman,

Assume this is the one and only pump, no backup unit next to it? Did this issue just show up or has it always been there?

As stated by others and your data....resonance/natural frequency issue

Imbalance in coupling or the pump can excite the natural frequency, not sure if you can balance the coupling to reduce the 1x vibration

Phase data, when you see 0 degrees where there should be 90 degrees, when you see 180 degrees where there should be 90, this is typical phase response to a resonant frequency more 0's and 180's than 90's

Position 1 has 3 times the vibration as position 2, whichever direction position 1 this is the direction with the issue and correction

To change a natural frequency, add mass, add stiffness, change machine speed, add dampening (cork,wood,rubber), dynamic absorber

Can you put a chain fall or come along on the motor and apply tension in the position 1 direction? Can you use the "eye" bolt locations on the motor to hang weight? Either of these two ideas should shift the natural frequency to reduce the vibration. 

Just because a bolt is tight does not mean it is clamping down tightly, meaning the bolt could be bottomed out and yet not touch the structure it is trying to hold. Motors TYPICALLY do not have a natural frequency issue. The adapter in you photo appears to be fairly stiff, what does the adapter bolt too? Either the adapter or the plate to which it is bolted are most likely the culprits of the natural frequency. If there is dirt in between the mating surfaces this too will change the natural frequency

Dave
Walt Strong

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Reply with quote  #19 
Best choice would be to bolt on a rigid steel weight. The basic approach is to decide how to mount the weight, pick a starting weight size, conduct impact test to determine the shift in natural frequency, calculate the final weight size, install weight and then conduct impact test.

My distant second choice would be to bolt on a dynamic mass absorber.

I could make more specific recommendations with additional information.

Don't screw around with wood, chains, come-along or damping materials for this type of structural vibration problem!

Walt
dnk

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Reply with quote  #20 
Have used dynamic absorbers several times on similar motors. Can be a quick & simple fix to use until you can make permanent changes.
Ron Stiemsma

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Reply with quote  #21 
I used the bolt holes for the lifting eye.  See attached.

 
Attached Files
docx DA.docx (845.33 KB, 20 views)

Walt Strong

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Reply with quote  #22 
Ron,

Good design! Was response primarily in one direction?

Walt
fburgos

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Reply with quote  #23 
I wonder what "design considerations" should be taken in account, mass of the motor? mass on the "dynamic absorber"
Batman

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Reply with quote  #24 
Thank you all for your valid comments. This is becoming very interesting.

Ron's solution is quite an easy quick fix until one can divulge deeper.

I wish to ask Ron roughly what mass was added in kgs and again roughly what was this mass as a percentage of the mass of the motor?

I'm trying to come up with a practical starting trial weight. 

For those who have asked, this pump is one of three and it's the one which has this particular behavior.

Thank you again.
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